Now what will be interesting to see is who can replicate this. Swapping M157 turbos onto the M278 makes the 550 models a great tuning value. Which tuner can facilitate the software for the swap though?

I was looking at a C218 CLS550 for a couple of years, it's amazing how the aftermarket has the potential to be great on the M278 but just falls short everywhere. A perfect example is catless downpipes for the 4Matic models (at least when I was looking), that your only option was the ridiculously expensive Weistec full exhaust system that came with downpipes. No one offered them for the AWD models due to fitment I guess.

I don't get why there isn't an MB tuner with a swap kit for the M278. It's like they purposely are missing a big part of the market.

I think tuners are more so concentrated on AMG models because they are built specifically for performance and therefore take less resources to develop kits for, opposed to a non AMG variant wich may have unknown weaknesses. I also think that tuners focus on AMG variants because they believe that thats the market that A) is interested mostly in performance kits and B) Have the willingness and ability to pay for the performance increases. They are wrong of coarse.

I think tuners are more so concentrated on AMG models because they are built specifically for performance and therefore take less resources to develop kits for, opposed to a non AMG variant wich may have unknown weaknesses.

Definitely truth to this but the M278 is basically a smaller M157. Swapping the turbos will expose what weakness exactly?

I think it is more that AMG owners are more willing to mod.

A turbo swap isn't a huge deal. Weistec told me they have done a few but no tuner advertises it as an off the shelf package.